It has been required that the image display surface of an image display device such as a liquid crystal display, a CRT display, a projection display, a plasma display or an electroluminescence display is imparted with abrasion resistance to avoid being scratched upon handling. To meet the request, in general, a hard coat film (an optical laminate), which comprises a hard coat (HC) layer provided on a substrate film or further imparted with optical functions such as anti-reflection properties and anti-glare properties, is used to increase the abrasion resistance of the image display surface of an image display device.
A hard coat layer is generally formed on a substrate film using a photopolymerizable resin such as heat-curable resin or an ultraviolet ray-curable resin. The thickness is adjusted according to the performance required for a hard coat film, preferably from 3 to 25 μm. However, a thin film having a layer thickness of about 3 to 25 μm cannot exhibit sufficient mechanical strength (pencil hardness) as affected by modification of a base substrate.
As a method of improving the hardness of a hard coat layer, there is a method of merely increasing the thickness of a hard coat layer. The hardness can be improved by increasing thickness, however, there are problems that cracking easily occurs in a hard coat layer, and curling occurs in a whole laminate due to curing shrinkage of components in the hard coat layer causing significant deterioration of workability upon applying the laminate on a display.
Also, as a method of improving the hardness of a hard coat layer, there is a method of adding inorganic fine particles. Generally, a hard coat film provided with a hard coat layer having inorganic fine particles added on a substrate film is produced (Patent Literatures 1 and 2).
However, in recent years, a hard coat film further excellent in abrasion resistance or hardness is required. It has been difficult for a hard coat film having a thickness of a hard coat layer capable of satisfying the required performance of a hard coat film to attain the mechanical strength by pencil hardness of 4 H or more even if inorganic fine particles are added in the hard coat layer.